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Sonata air conditioner problem

My 2006 Hyundai Sonata GLS V-6, 81K miles, has an air conditioner problem. The symptom is this: On hot days, when the car has been parked in the sun, turning on the A/C usually will not turn on the compressor. So, if I wait 5 minutes, hot air is still coming out. If I turn the switch off and on a few times, often it will come on with the third for fourth try, then the compressor will shut off intermittently. Here is the history:
Summer 2009, with about 57K miles, took it to dealer, they found refrigerant low and recharged it. Problem seemed fixed for a little while, then returned next summer.

Summer 2010, took it back to them, they said refrigerant pressure was too high and bled some. Problem really not fixed, but days started cooling off so they could not reproduce the problem.

Summer 2011, now out of warranty, so took it to reputable local mechanic. They identified a faulty compressor clutch thermostat and replaced it. Problem continues now that hot weather has returned. Note that in morning, before car has been in hot sun, the A/C works OK.

The first thing I’d want to know is whether or not 12V is actually being sent to the compressor at those hot times when it doesn’t turn on. If it gets the 12V then this leaves you with the actual A/C system and you trace the issue in that direction.

If it doesn’t get 12V then its just a basic power supply problem perhaps having something to do with a failing switch or relay. Often when electrical parts are on their way out they show their issues first when they get hot.

Stay away from that dealer. It sounds like they don’t have anyone that knows what they are doing. Most shops will mess with A/C systems, but there are some shops that specialize in HVAC. You might find one of those is you’re not going to chase it yourself.

Makes sense. Sharing this info with my mechanic.